Implantable medical devices (IMDs), such as implantable cardioverter-defibrillators, may implement a variety of tachyarrhythmia detection and analysis algorithms. In some examples, IMDs may implement rate-based detection and analysis algorithms in order to detect and analyze tachyarrhythmias. IMDs may also implement template matching algorithms in order to determine the morphology of a detected tachyarrhythmia and to further classify the tachyarrhythmia. IMDs may provide therapy based on conclusions drawn from the use of these rate-based detection and template matching algorithms.
An IMD that implements a rate-based detection algorithm may monitor the length of intervals between sensed ventricular or atrial events, and detect a tachyarrhythmia when a predetermined number of those intervals are shorter than a programmed time interval. In some examples, IMDs may perform further analysis of tachyarrhythmias using rate information. For example, IMDs may characterize tachyarrhythmias based on the range of values in which the intervals fall, the stability of the intervals, and the average or median values of the intervals.
An IMD that implements a template matching algorithm may analyze the morphology of beats within a tachyarrhythmia by comparing the beats to a template that represents a particular beat morphology (e.g., a normal beat morphology). The IMD may determine whether each of the individual beats is similar or dissimilar to the template during the comparisons. After the comparisons, the IMD may identify the type of tachyarrhythmia based on how many of the beats included in the tachyarrhythmia are similar or dissimilar to the template beat morphology.